Many present day electronic and electrical devices are powered by a rechargeable battery or battery pack. This is particularly true in certain fields, such as portable communications devices including cellular telephones, for example. Rechargeable batteries are preferred in such applications because of the cost advantage over non-rechargeable batteries, since a rechargeable battery can be used and recharged often up to several hundred times.
Unfortunately, it is often the case that the battery used with portable communications device significantly adds to the volume and weight of the device. In many markets for such products, size and weight are key market features, and the emphasis in designing these products is to reduce the battery size. There are several design strategies that are used working towards this goal. Chief among these is to reduce the power requirements of the device, therefore allowing a smaller battery to be used without significantly reducing the operation time afforded by the battery. In certain markets, another strategy is to reduce the charging time of the battery. Typically, the time required to charge a battery is longer than the user of the device can wait for the battery to be recharged. For this reason, users of portable devices have come to expect "all day" operation times from a single battery, or they must purchase and carry an additional battery or batteries. However, an "all day" sized battery is typically larger than preferred, and purchasing additional batteries is likewise a non-optimal solution.
To solve this problem many manufacturers have begun to offer so called turbo or ultrafast charging technology. This is the technology used to recharge a battery in, typically, about 15 to 30 minutes. With such a short charging time, a battery can be recharged during brief inactivity periods when mobility is not essential, such as while driving between business appointments, or during a typical "coffee break". To accomplish recharging in such time, it is necessary to increase the electrical current applied to the battery during recharging. This presents a significant problem to many battery designs.
Often a rechargeable battery is provided with two sets of electrical contacts; one set for providing power to it's associated device, and a second set for receiving electric current from a charger. Additionally, the charger contact set often includes contacts for the charger to electrically connect with sensors in the battery, such as thermal sensors, for example. Since the charger contact set is usually exposed when the battery is mounted on it's associated device to allow coupling to a charger while mounted on the device, there exists the potential for a conductive element to contact both the positive and negative charge contacts. This can happen when, for example, a cellular phone battery is carried in a person's pocket with keys, change, and so on. Shorting the battery in such a scenario can result in injury to the person. To avoid such an event, a simple and cost effective solution is to provide a diode in the charging path of the battery, between the charging contacts and the battery cells inside the battery pack. This diode allows for charging current to pass through the cells, but prevents the cells from discharging through the charging contacts.
This charging diode is problematic in considering ultrafast charging because the high electric current used in this sort of charging causes the diode to heat significantly. This can, at the very least, interfere with charge schemes based on temperature and changes in temperature, and at an extreme, can create hot spots on the battery, or even melt battery components. The now conventional solution to this problem is to replace the charging diode with a transistor switch. This transistor switch is preferably a MOSFET type, and is actuated in response to the charger making electrical contact with the sensors in the battery pack, such as, for example, a thermistor or a code resistor. Two excellent references on the topic are U.S. Pat. No. 5,471,128 to Patino et al., and U.S. Pat. No. 5,576,612 to Garrett et al., both of which describe circuits using MOSFETs to replace charging diodes.
However, the prior art does not address the problem of how to identify a battery endowed with such a high rate protection circuit. Batteries including the high rate protection circuit are significantly more expensive to build, and therefore manufactures charge a premium for them. Often it may be the case that the capacity of the turbo or ultrafast battery including the high rate protection circuit is the same or similar to a standard battery also offered for sale. Obviously the standard battery, protected by a charging diode, should not be charged at an ultrafast rate. Conversely, if a battery designed for ultrafast charging is not charged at an ultrafast rate, the purchaser of the battery has not received any benefit for the premium paid for the battery. Therefore, there is a need for a means and method by which a charger can distinguish an ultrafast rate capable battery from a standard rate battery of equal or similar capacity.